1. Technical Field
The present invention relates generally to electrosurgical systems. In particular, the present invention relates to electrosurgical return electrodes that are adapted to increase the comfort level of a patient positioned thereon. More specifically, the present invention relates to electrosurgical return electrodes that include both pressure sore reduction and heating capabilities.
2. The Relevant Technology
In the area of electrosurgery, medical procedures of cutting tissue and/or cauterizing leaking blood vessels are performed by utilizing radio frequency (RF) electrical energy. As is known to those skilled in the medical arts, electrosurgery is widely used and offers many advantages including that of the use of a single surgical tool for both cutting and coagulation. The RF energy is produced by a wave generator and transmitted to a patient's tissue through a hand-held electrode that is operated by a surgeon. For historical perspective and details of such techniques, reference is made to U.S. Pat. No. 4,936,842, issued to D'Amelio et al., and entitled “Electrosurgical Probe Apparatus,” the disclosure of which is incorporated by this reference.
Every monopolar electrosurgical generator system must have an active electrode that is applied by the surgeon to the patient at the surgical site to perform surgery and a return path from the patient back to the generator. The active electrode at the point of contact with the patient must be small in size to produce a high current density in order to produce a surgical effect of cutting or coagulating tissue. The return electrode, which carries the same current as the active electrode, must be large enough in effective surface area at the point of communication with the patient such that a low density current flows from the patient to the return electrode. If a relatively high current density is produced at the return electrode, the temperature of the patient's skin and tissue will rise in this area and can result in an undesirable patient burn. According to the Emergency Care Research Institute, a well-known medical testing agency, the heating of body tissue to the threshold of necrosis occurs when the current density exceeds 100 milliamperes per square centimeter. Furthermore, the Association for the Advancement of Medical Instrumentation (“AAMI”) has published standards that require that the maximum patient surface tissue temperature adjacent an electrosurgical return electrode shall not rise more than six degrees) (6°) Celsius under stated test conditions.
Over the past thirty years, industry has developed products in response to the medical need for a safer return electrode in two major ways. First, they went from a small, about 12×7 inches, flat stainless steel plate coated with a conductive gel placed under the patient's buttocks, thigh, shoulders, or any location where gravity can ensure adequate contact area to a flexible electrode. These flexible electrodes, which are generally about the same size as the stainless steel plates, are coated with a conductive or dielectric polymer and have an adhesive border on them so they will remain attached to the patient without the aid of gravity. Upon completion of the electrosurgical procedure, these flat flexible electrodes are disposed of By the early 1980's, most hospitals in the United States had switched over to using this type of return electrode. These return electrodes are an improvement over the old steel plates and resulted in fewer patient return electrode burns but have resulted in additional surgical costs in the United States of several tens of millions of dollars each year. Even with this improvement, hospitals were still experiencing some patient burns caused by electrodes that would accidentally fall off or partially separate from the patient during surgery.
Subsequently, there was proposed a further improvement, an Electrode Contact Quality Monitoring System that would monitor the contact area of the electrode that is in contact with the patient and turn off the electrosurgical generator whenever there was insufficient contact area. Such circuits are shown, for example, in U.S. Pat. No. 4,231,372, issued to Newton, and entitled “Safety Monitoring Circuit for Electrosurgical Unit,” the disclosure of which is incorporated by this reference. This system has resulted in additional reduction in patient return electrode burns, but requires a special disposable electrode and an added circuit in the generator that drives the cost per procedure even higher. Twenty years after this system was first introduced, fewer than 40 percent of all the surgical operations performed in the United States used this system because of its high costs.
Although various advances have been made in the electrosurgical arts, there remains room for improvement. More particularly, while systems and devices have been developed to increase the safety of patients undergoing electrosurgical procedures, such as by reducing the number of patient return electrode burns, the comfort of these patients before, during, and after electrosurgical procedures remains lacking.
One cause of patient discomfort is the relatively low temperatures maintained in hospitals and particularly in operating rooms where electrosurgical procedures take place. Operating room temperatures are typically maintained between about 18.5-21° C. (65.3-69.8° F.). For many patients, this temperature range feels too cold. Additionally, during a surgical procedure patients may contact objects that have physical properties that cause the objects to feels even colder than they really are. For example, metal operating room tables and return electrodes may be good thermal conductors. The thermal conductivity of operating room tables or return electrodes causes heat to be readily conducted away from a patient when the patient makes contact with the operating room table or return electrode that is within the above temperature range. The transfer of heat from the patient to the operating room table or return electrode causes the patient to feel even colder than the operating room temperature, thereby increasing the patient's discomfort.
Some common solutions for warming patients include the use of heated air or fluid circulation systems. Heated circulation systems can be incorporated into pads that are positioned underneath or on top of a patient during a surgical procedure. The circulation systems commonly include tubes or conduits through which air, water, or another fluid can be circulated. These systems also include a pump to circulate the fluid or air as well as a heating element for heating the air or fluid before it is circulated through the tubes or conduits. While such systems may provide heat to a patient during a surgical procedure, the systems also suffer from drawbacks. For example, heated circulation systems typically do not provide even heating to the patient. Rather, the temperature in the areas directly adjacent to the tubes or conduits is often significantly higher than the areas between the tubes or conduits.
Another common solution for warming patients includes the use of one or more heated blankets. The heated blankets may be draped over a patient or positioned between the patient and the operating room table, for example. The heated blankets may be electric heating blankets or blankets made of cotton or wool that has been warmed in a warming box.
Drawbacks and difficulties are encountered with the use of both electric heating blankets and warmed blankets. For example, blankets warmed in a warming box maintain their temperature for a relatively short period of time. Once they have cooled off, the blankets must be replaced with freshly warmed blankets. It can be inconvenient to replace blankets during an electrosurgical procedure, especially when the blankets must be replaced multiple times during a lengthy procedure. Furthermore, because of the difficulty in moving and repositioning a patient during an electrosurgical procedure, it can be impractical to replace cooled blankets when they are placed between the patient and the operating room table. Additionally, a sterile field must be maintained throughout a surgical procedure. Replacing cooled blankets during a surgical procedure may compromise the sterile field, which can lead to patient infection and other complications. Moreover, blankets that are draped over a patient, whether heated or warmed, may move or fall off of the patient during the procedure, thereby requiring additional attention from operating room personnel.
Cold temperatures are not the only cause of discomfort to patients undergoing electrosurgical procedures. Rather, it is well known in the medical field that patients may develop decubitus ulcers, also known as pressure sores during a prolonged period of immobility. Typically, pressure sores develop in elderly patients who are confined to their beds or otherwise have limited movement. The pressure sores arise in those areas of the patient's body where a prolonged pressure is applied to the patient's tissue, usually over an underlying bony prominence. The prolonged pressure causes ischemic damage and tissue necrosis due to the maintenance of blood pressure above the normal capillary blood pressure of 32 mmHg. Although pressure sores typically occur in those patients who remain in one position for an extended period of time, pressure sores may arise from application of an intense pressure applied over a short period of time, approximately two hours, to a localized area, such as during various surgical procedures.
Generally, to prevent pressure sores a patient is placed upon a pressure reducing mattress or pad during a surgical procedure to reduce or substantially eliminate the forces applied to the sensitive areas of the body where tissue covers underlying bony prominences. One device that may be used to prevent pressure sores in an operational scenario is a foam pad, approximately 3-4 inches in height, which is placed between the operating table and the patient. Although foam pads have many advantages, such as being inexpensive and lightweight, they provide minimal relief to the patient while trapping body heat that may aid in generating pressure sores. Furthermore, by trapping heat the foam pad may aid in increasing the patient's tissue temperature so that during an electrosurgical procedure the tissue temperatures may rise above the six degrees) (6°) Celsius temperature rise threshold established by the AAMI. Additionally, foam pads are typically discarded after a surgical procedure since they are difficult to sterilize and clean. Furthermore, the material forming the foam pad may release lethal fumes if ignited during a fire.
An alternate pressure reducing mattress or pad is a layer of sheepskin placed on the operating table. Unfortunately, sheepskin provides poor protection to the patient and does not effectively distribute the patient's pressure throughout the entire surface upon which they are laying. As with the foam pad discussed above, sheepskin is difficult to sterilize and clean following a surgical procedure.
Yet another type of pressure reducing device is the air inflated mattress that includes a vinyl sleeve filled with air to a desired pressure. Unfortunately, the air mattress must be significantly pressurized to prevent the patient from touching the bottom surface upon which the mattress is placed. In the event the patient touches the bottom surface, there is a chance for development of a pressure sore. Additionally, in order to maintain the required pressure, typically, a pump is connected to the mattress to monitor the pressure of air contained within the mattress and pump additional air into the mattress as required. With a patient placed upon the movable air mattress, which is in turn resting upon an operating table, the patient is lying upon two flexible surfaces. The patient is thereby placed in an unstable and precarious position during surgical procedures. Additionally, air-type mattresses are expensive to maintain due to the need for a pump to maintain the required air pressure. Furthermore, the air mattress may easily be perforated, thereby leaking air and reducing the effectiveness of the mattress to maintain the patient distal from the surface upon which the mattress is placed.
A similar pressure-reducing device to the air filled mattress is the water type mattress. The water-type mattress has a similar form to that of the air mattress; however, water is pumped through the mattress rather than air. Unfortunately, the water type mattress suffers from many of the limitations of the air type mattress. Additionally, in the event that the water mattress leaks, a large amount of water would be discharged onto the floor surrounding the patient, thereby making it dangerous for individuals to walk and work in close proximity to the patient.
Although many of the above-described limitations are alleviated in general use within a hospital, each recited pressure sore device has various drawbacks with respect to their use during electrosurgical procedures. For example, in the event a foam type mattress is used during an electrosurgical procedure, there is a chance that the foam pad may ignite, thereby burning the patient and also emitting lethal fumes within the operating theater.
With respect to the air and water type mattresses, inclusion of the required pumps to maintain the desired pressure for a long period of time increases the amount of equipment necessarily stored within an operating theater. With more equipment within the limited space, the ability of the surgeon to move around is reduced. In the event of a water leak from the water mattress, there is the possibility that of electrocution of the patient and/or the physicians and nurses in the operating theater, as well as the possibility of shorting of the electrosurgical return electrode.
Therefore, it would be an advance in the present electrosurgical art to provide an electrosurgical return electrode that is self-limiting, while increasing the comfort of the patient by providing heating capabilities and reducing the likelihood of pressure sore creation.